The invention relates to a device for reducing distortions in layer images of a three-dimensional object formed by means of penetrating radiation.
From German Offenlegungsschrift No. 28 10 608 it is known to record individual perspective images either separately or as a superposition image and to displace and superpose these images in a suitable manner in order to form layer images. In order to reduce artefacts in the reconstructed layer image, corresponding points of the perspective images are examined in order to determine whether they belong to the selected layer, in which case they have to be displayed as common layer image points, or whether they do not belong thereto, in which case they are ignored for the imaging. Prior to the mutual comparison, the perspective images can also be filtered, so that the low spatial frequency components are attenuated (see Joseph W. Goodman, "Fourier Optics", McGraw-Hill, 1968, page 147, second paragraph).
The known method, where the absolute gray values are derived from corresponding points in the perspective images recorded by means of only one group of radiation source positions, offers better results as the contrast of the perspective images is higher. This method, therefore, is suitable mainly for angiographic examinations where the object structures to be examined are accentuated by means of a contrast medium. It is assumed that several of such object structures are not superposed in the perspective images, because otherwise the contrast would be less.